QTR-Quadtone RIP

You can brute force calibrate the ED100 by using Wolf's IT8.
His data that comes with the target gives all the info you need.
The basic approach is this:

    1--Read the 23 step grayscale and note all three values for each
       step.
    2--Convert to decimal.
    3--Using the known RGB/CMY values from Wolf and the Y cie value
       along with the readings,use cubic spline interpolations to
       get the appropriate density numbers. You would use the Y cie     
       values and interpolation from the Green readings to get the
       proper values to first convert to Lab L* and then to d'log
       visible if that is what you wish.You can get the formulas
       for the Lab and d'log transforms online.

Note that if you plot the relationships of readings to known values 
you will see what looks somewhat like a geometric curve so the
instrument is not linear. Hence the cubic splines. To extrapolate each
extreme beyond the IT8 data you can use the slopes of the last and
first two points.This will offer reasonable accuracy in those areas.
The instrument is quite precise (with some deficits).

Now for the bad news. The densitometer is extremely sensitive to UV
induced fluorescence in papers so surrounding light can and will
influence readings at both extremes and can be severe. The only way I
found to overcome this is to cover the sample and instrument with a
dark cloth while making readings. It does have a very good dynamic
range so if you have the standards you can get very high density
readings with it. It also is very repeatable.

I have 2 of the ED100s and use them for B&W with QTR. They have proved
to be more accurate than the process densitometer I paid 100s of $ for
 some years ago.I would be very pleased if I could find a way to get
them to store readings for later transfer as they apparently are
capable of doing.

Hope this is of some help to you.

Regards
Duane






--- In QuadtoneRIP@yahoogroups.com, "Tom Moore" <r.t.moore@...> wrote:
>
> It looks like the device you have is reading RGB density. The x-rite
> 810 (that I have) also does this. In the case of the 810, the density
> readings are performed according to a standard called Status-A density
> readings. The 810 also will take Visual density readings. These are
> the usual density values we refer to in BW printing. I have not been
> able to find a way to mathematically relate RGB density to Visual
> density. I tried simple averaging and various more complicated
> correlation techniques. Nothing was satisfactory. I quit looking once
> I realized that the Status-A RGB values bear no relationship to the
> RGB values used by Photoshop, for example.
> 
> Your best bet would be to determine if there is a setting on your
> densitometer for Visual density.
> 
> Tom Moore
> 
> --- In QuadtoneRIP@yahoogroups.com, "andywebsterus" <andy@> wrote:
> >
> > OK I know I'm answering my own posts!
> > 
> > > Toolcrib will auto-paste these values into Excel....  (looked like
> I was 
> > > getting somewhere) like this:
> > > 
> > > MGI RD-200 000255 
> > 
> > The useful part of this string are the values:
> >  
> > 00095B          00077A              00301A
> > 
> > They are R-G-B as HEX values.
> > 
> > I can get all the measurements neatly and automatically into Excel, 
> > (each click on the densi pastes another reading into the sheet) then 
> > converted to decimal.  The lower the number the more reflective the 
> > surface.
> > 
> > 
> > How do I convert these  decimal RGB values into something that QTR 
> > will enjoy?
> > 
> > RGB to L ?  How to do that?
> > 
> >  I Have an IT8 target (Wolf Faust) which I might be able to use to
> check 
> > calibration...
> > 
> > Andy
> >
>